The effect of subsea infrastructure self-weight and pipeline in-service horizontal loading on the consolidated undrained capacity of deep-water shallow foundations was investigated by means of fully coupled three-dimensional finite-element analyses. The results show that the undrained uniaxial and combined capacity increase under horizontal preloading and over realistic in-field loading time regimes. The gain in undrained capacity is quantified through simple equations incorporating a critical state soil mechanics framework and is defined as a function of magnitude and duration of vertical and horizontal preload, foundation embedment ratio and soil-skirt interface roughness.